Imaging in anterior glenohumeral instability

In the shoulder, the advantages of range of motion are traded for the disadvantages of vulnerability to injury and the development of instability. Glenohumeral instability encompasses a broad spectrum of clinical complaints and presentations. The diagnosis can be obvious or entirely unsuspected. Imaging findings depend on numerous factors and range from gross osseous defects to equivocal labral abnormalities and undetectable capsular lesions. This review focuses on the imaging findings in three distinct clinical scenarios: acute first-time shoulder dislocation, chronic instability with repeated dislocation, and chronic instability without repeated dislocation. The biomechanics of dislocation and the pathophysiology of labral-ligamentous injury are discussed. The authors distinguish the findings that occur in the acutely traumatized shoulder from those that typify the chronic unstable joint. The roles of different imaging modalities are also distinguished, including magnetic resonance arthrography and the value of specialized imaging positions. The goal of imaging depends on the clinical scenario. Image interpretation and reporting may need to emphasize diagnosis and the identification of lesions that are associated with instability or the characterization of lesions for treatment planning.